The invention is based on a hydraulic brake system for road vehicles.
German Patent 40 29 793 A1 makes known a brake system of this kind, in which at the start of braking, the first stop valve in the brake circuit remains in the open position, so that by means of actuating the brake pedal, pressure fluid is displaced from the pressure chamber of the master cylinder, and brake pressure is increased in the wheel brake cylinder. The brake pedal executes a deflection, which is predominantly determined by the air play in the wheel brake, as well as by the elasticity of the wheel brake and the brake line. However, the generally desired progressive pedal characteristic, i.e. the resistance that at the onset of pedal travel is slight and progressively increases with greater deflection, is unsteady in the known brake system, in that from a predetermined pressure threshold, the first stop valve is switched to the closed position and the power actuation of the service brake is activated. As the load exerted by the driver increases, the brake pedal has no further significant travel. It is, however, desirable for approximately the same pedal characteristic to prevail, both upon actuation of the service brake as well as upon actuation of the emergency brake.